Unsaturated carboxylic acids such as acrylic acid and methacrylic acid used as raw materials for various chemicals can be produced by a two-stage reaction using unsaturated aldehydes as intermediate products. Since a demand for both of acrylic acid and methacrylic acid continues to increase steadily, efforts have been intensively made at improving catalysts used in the production thereof.
On the other hand, a demand for butadiene, which is an important raw material for chemicals to be used as a raw material for synthetic rubbers and the like, has steeply increased as a raw material for energy-saving type automobile tires owing to global augmentation in demand for automobiles and increase in awareness of environmental issues in recent years. However, since the production of C4 fractions has decreased, the shortage of butadiene production has continued. Thus, it is forecasted that the shortage of butadiene supply should be further accelerated hereafter. Therefore, it has been strongly desired to industrialize a novel process for producing butadiene.
A process for producing an unsaturated aldehyde and/or an unsaturated carboxylic acid by a selective oxidation reaction of an unsaturated hydrocarbon in a fixed bed reaction apparatus with a complex metal oxide catalyst having molybdenum as an essential ingredient has been well known. Moreover, a process for producing butadiene from n-butene in a fixed bed reaction apparatus using a complex metal oxide catalyst having molybdenum as an essential ingredient has been also well known.
The shape of the catalyst for use in the fixed bed reaction apparatus is selected depending on its use but catalyst shapes such as a ring shape, a cylinder shape, a tablet shape, a honeycomb shape, a trefoil shape, a quatrefoil shape, and a spherical one have been frequently used. Of these, a spherical catalyst has been widely used due to easiness of an operation of packing the catalyst into a reaction tube and an operation of extracting the catalyst after use from the reaction tube.
Moreover, a method of supporting a catalyst-active ingredient on an inert support has been industrially widely used to produce the supported catalyst for the purpose of suppressing a decrease in selectivity for a target product by a successive reaction and reducing heat accumulation in a catalyst layer in a reaction in which heat generation is involved. Particularly, in the case where a target product is selectively produced by an oxidation reaction or an oxidative dehydrogenation reaction of an organic compound, the supported catalyst is used as an effective method.
As a process for producing a spherical supported shaped catalyst, Patent Document 1 discloses a process for producing a catalyst for producing acrolein and/or acrylic acid from propylene and Patent Document 2 discloses a process for producing a catalyst for producing methacrolein and/or methacrylic acid from isobutylene and/or tertiary-butyl alcohol.
In Patent Documents 1 and 2, as a process for producing a spherical shaped catalyst, a production process by a tumbling granulation method is disclosed. Specifically, a spherical support necessary for attaining a desired catalyst diameter is placed in a tumbling granulation apparatus and a liquid as a binder and a catalyst-active ingredient and/or a precursor thereof are sprinkled on the support with rotating the shaping machine, thereby producing the spherical shaped catalyst.
As mentioned above, a process for producing butadiene from n-butene is known. For example, in Patent Documents 3 and 4, processes of oxidative dehydrogenation in the presence of a complex metal oxide catalyst containing molybdenum, bismuth, iron, and cobalt as main ingredients have been described. However, from the standpoints of catalyst activity, butadiene selectivity, stability of reaction operation, catalyst life, catalyst production, and the like, conventional catalysts are industrially insufficient and an improvement thereof has been strongly desired.
Moreover, in Patent Document 5, there is a description of a supported catalyst that is produced in the presence of a pore-forming agent and a production thereof in an industrial scale is also described.